[6] In August 890, at the Diet of Valence, a council of bishops and feudatories of the realm, after hearing the recommendation of the pope, and receiving notification of Charles the Fat's previous agreement to the proposition, proclaimed Louis as king in Lower Burgundy and Provence.

Since he was still young, local barons elected Ermengard to act as his regent, with the support of Louis's uncle, Richard the Justiciar.

Throughout his reign he fought with these Saracen pirates, who had established a base at Fraxinet in 889 and had been raiding the coast of Provence, alarming the local nobility.

[11] However, his inability to stem the Magyar incursions and impose any meaningful control over northern Italy saw the Italian nobles quickly abandon his cause and once again align themselves with Berengar.

[12] In 905, Louis, after again listening to the Italian nobles who were tired of Berengar's rule, this time led by Adalbert I of Ivrea,[13] launched another attempt to invade Italy.

[12] Once again throwing Berengar out of Pavia,[10] he marched and also succeeded in taking Verona[12] with only a small following, after receiving the promise of support from the bishop, Adalard.

After this last attempt to restore his power over Italy, Louis continued to rule Provence for over twenty years, though his cousin[14] Hugh, count of Arles, was the dominant figure in the territory.

[13] In 899, Louis III was betrothed to Anna of Constantinople, the daughter of Byzantine Emperor Leo VI the Wise and his second wife, Zoe Zaoutzaina.

[16] The evidence for this is a letter by Patriarch Nicholas Mystikos in which he testifies that Leo VI had united his daughter to a Frank prince, a cousin of Bertha, to whom came later a great misfortune.

There has been modern speculation, proposed by Previté-Orton and championed by Christian Settipani, that she was Anna,[20][7]the daughter of Leo VI and Zoe Zaoutzaina, based both upon the documented betrothal, as well on the onomastic evidence, stating that Charles-Constantine's name points to a Byzantine mother.

Richer specifically stated that Charles' ancestry was tainted with illegitimacy and mentioned nothing of his mother's supposed illustrious Byzantine parentage.